Power over Ethernet (PoE), which is outlined in IEEE Std 802.3-2005 clause 33 (the PoE Standard), refers to a technique for delivering power and data to an electronic device via Ethernet cabling. PoE eliminates the need for a separate power source to deliver power to attached powered devices. In a PoE system, a power sourcing equipment (PSE) device provides a power supply to electronic devices, which may be referred to as powered devices (PDs), via an Ethernet cable. Such PDs may include voice over Internet protocol (VoIP) telephones, wireless routers, security devices, network devices, field devices to monitor process control parameters, data processors, other devices, or any combination thereof.
The PSE device uses a PD detection operation to detect when a PD is coupled to a port of the PSE device, before the PSE device provides a power supply to the particular port. The PoE Standard also specifies that a PD that draws less than 10 mA of port current for a certain period of time is deemed to be disconnected, and the PSE device can discontinue the power supply to the particular port. Accordingly, PSE devices often monitor a current drawn by the PD using an analog-to-digital converter (ADC) circuit. However, such ADC circuits can be expensive and can be insensitive to current pulses of short duration, depending on the sampling rate of the ADC circuit, which current pulses may be drawn by the PD.
Hence, there is a need for circuitry to detect when a PD is disconnected from a port. Embodiments disclosed herein can provide solutions to these and other problems, and offer other advantages over the prior art.